“Percy Jackson: Sea of Monsters,” the sequel to 2010’s “Percy Jackson & the Olympians: The Lightning Thief,” falls into that category. The movie offers the kind of perfectly pleasant but utterly forgettable entertainment that would have made for a satisfying night of television, but falls flat on the big screen. You’ll be content, but you won’t be thrilled.

For those who didn’t see the original, the movie follows the adventures and general monster-slaying done by the modern day children of Greek gods. Technically, it’s based on a popular series of young adult novels by Rick Riordan, but the movies change so much that fans of the books will inevitably be disappointed.

If you’re not familiar with the series, a basic knowledge of Greek myths (and their tendency to have affairs with random humans who inevitably give birth to heroes) will be enough to help you not get lost. A lengthy voiceover at the beginning of the movie fills in the rest.

The cast is all perfectly fine at their jobs, and largely quite attractive to look at. As Percy Jackson, Logan Lerman manages to bring some depth of feeling to his complicated relationships with both his absent godly father and his cyclops half-brother.

Douglas Smith is quite sweet as the cyclops in question, and Brandon T. Jackson brings some much-needed spark to the movie as a satyr named Grover. It was nice hearing Ron Perlman’s voice as a villainous cyclops, but the earlier “Pacific Rim” used his weirdness to much better effect.

The movie’s biggest strength, however, is the fact that it’s surprisingly funny. Nathan Fillion makes the most of his one long, hilarious scene as the god Hermes, and Stanley Tucci has some great moments as Dionysus, the god of wine.

Jake Abel also has quite a bit of fun as the movie’s primary villain, his dry delivery turning potentially terrible dialogue into wonderfully funny one-liners that make him seem so much smarter than anyone else in the room.

Since this is an adventure film, however, they often interrupt the jokes to have the characters fight various monsters. The computer-generated imaging is adequate, if not stunning, and was best used for a mechanical bull that tears up the campground just because it can.

The fight scenes are decently choreographed, though they offer so few surprises that even their “shocking moments” come straight out of the TV-adventure-movie playbook.

There are no great cinematic crimes in this movie, but there are also no great successes. It’s the textbook example of an utterly average movie, not good enough to be loved and not bad enough to be hated.

It’s a safe-enough option for families looking for something to do. Kids should be suitably entertained for the nearly two-hour running time, and adults can distract themselves with trying to figure out how many different animals went into making that scorpion-tailed creature that’s running around.

When it’s over, you’ll start to forget the movie the moment you walk out of the theater. But when it crops up on TV one evening at some distant point in the future, you probably won’t mind watching it again.